An induced pluripotent stem (iPS) cell is a cell generated by transferring a defined nuclear reprogramming factor to a somatic cell to confer pluripotency to the somatic cell. The term pluripotency refers to the potential for differentiating into a wide variety of tissues; it is believed that tissue degenerative diseases such as Parkinson's disease and juvenile diabetes, as well as traumas such as spinal injuries, can be treated by using this property.
Traditionally, ES cells (embryonic stem cells), which likewise possess pluripotency, have been attracting attention as a resource for regenerative medicine. However, ES cell transplantation can cause graft rejection because it is a form of allotransplantation, and has been viewed as posing ethical problems, including destructive use of human embryos and employment of abortive fetuses. In contrast, iPS cells, which are generated using somatic cells, can be thought to have resolved these problems, and are expected to be highly useful as a resource for regenerative medicine in the future.
As such, iPS cells have been established mainly in mice and humans (see patent documents 1-2, and non-patent documents 1-3). Human IFS cells cannot be applied clinically until their safety and efficacy are previously assured by animal experimentation. However, small animals, such as mice and rats, do not permit long-term follow-up examination after undergoing cell transplantation because of their short longevity. While it seems ideal that at least 5 years be secured for the examination, the longevity of the mouse is up to 1 to 2 years.
Meanwhile, the dog is a laboratory animal that can easily be handled, lives long, and is similar to humans in many features, both anatomically and physiologically. The longevity of the dog is at least 10 years, sufficient for a length of follow-up examination. The dog also permits easier mass-breeding than other large animals. For this reason, the dog is the laboratory animal best suited for determining the clinical applicability of human IFS cells; the experimental results obtained by transplantation of IFS cells to dogs are believed to be highly useful. To this end, it is necessary to generate a canine iPS cell; however, no reports are available on actual establishment thereof.    patent document 1: WO 2007/069666    patent document 2: WO 2008/118820    non-patent document 1: Takahashi, K. et al., Cell, 126(4): 663-676 (2006)    non-patent document 2: Takahashi, K. et al., Cell, 131: 861-872 (2007)    non-patent document 3: Yu, J. et al., Science, 318: 1917-1920 (2007)